a) Internal resistance

a) source of e.m.f.; internal resistance

b) terminal p.d.; lost volts

ci) the equations ε = I(r + V) and ε = V + r

terminal p.d. = the p.d. measured across the terminals of the e.m.f. source

internal resistance = the resistance within an e.m.f. source

current in an e.m.f. source → source transfers chemical energy to the electrical store of the charge carriers → some chemical energy is dissipated into thermal energy → internal resistance → lost volts

• → terminal p.d. < e.m.f.

• → e.m.f. = terminal p.d. + lost volts

• when current is 0A → e.m.f. = terminal p.d.

lost volts = Ir

• lost volts (V) = current (A) × internal resistance (Ω)

ε = I(R + r)

• e.m.f. (V) = current (A) × (resistance (Ωs) + internal resistance (Ω))

ε = V + Ir

• e.m.f. (V) = terminal p.d. (V) + (current (A) × internal resistance (Ω))